1. Field of the Invention
Embodiments of the present invention generally relate to solar cells and methods and apparatuses for forming the same. More particularly, embodiments of the present invention relate to thin film multi-junction solar cells and methods and apparatuses for forming the same.
2. Description of the Related Art
Solar cells convert solar radiation and other light into usable electrical energy. The energy conversion occurs as the result of the photovoltaic effect. Solar cells may be formed from crystalline material or from amorphous or micro-crystalline materials. Generally, there are two major types of solar cells that are produced in large quantities today, which are crystalline silicon solar cells and thin film solar cells. Crystalline silicon solar cells typically use either mono-crystalline substrates (i.e., single-crystal substrates of pure silicon) or a multi-crystalline silicon substrates (i.e., poly-crystalline or polysilicon). Additional film layers are deposited onto the silicon substrates to improve light capture, form the electrical circuits, and protect the devices. Thin-film solar cells use thin layers of materials deposited on suitable substrates to form one or more p-n junctions. Suitable substrates include glass, metal, and polymer substrates. It has been found that the properties of thin-film solar cells degrade over time upon exposure to light, which can cause the device stability to be less than desired. Typical solar cell properties that may degrade are the fill factor (FF), short circuit current, and open circuit voltage (Voc).
Problems with current thin film solar cells include low efficiency and high cost. Therefore, there is a need for improved thin film solar cells and methods and apparatuses for forming the same in a factory environment. There is also a need for a process which will fabricate high stability p-i-n solar cells having high fill factor, high short circuit current, high open circuit voltage and good device stability.